A photomicrograph of superficial keratinocytes or skin cells. Credit: Thomas Deerinck, National Center for Microscopy and Imaging Research, UC San Diego. |
The
biological mechanism of sunburn—the reddish, painful, protective immune
response from ultraviolet (UV) radiation—is a consequence of RNA damage
to skin cells, report researchers at the University of California, San
Diego School of Medicine and elsewhere in the July 8, 2012 Advance
Online Publication of Nature Medicine.
The
findings open the way to perhaps eventually blocking the inflammatory
process, the scientists said, and have implications for a range of
medical conditions and treatments.
“For
example, diseases like psoriasis are treated by UV light, but a big
side effect is that this treatment increases the risk of skin cancer,”
said principal investigator Richard L. Gallo, MD, PhD, professor of
medicine at UC San Diego School of Medicine and Veterans Affairs San
Diego Healthcare System. “Our discovery suggests a way to get the
beneficial effects of UV therapy without actually exposing our patients
to the harmful UV light. Also, some people have excess sensitivity to UV
light, patients with lupus, for example. We are exploring if we can
help them by blocking the pathway we discovered.”
Using
both human skin cells and a mouse model, Gallo, first author Jamie J.
Bernard, a post-doctoral researcher, and colleagues found that UVB
radiation fractures and tangles elements of non-coding micro-RNA—a
special type of RNA inside the cell that does not directly make
proteins. Irradiated cells release this altered RNA, provoking healthy,
neighboring cells to start a process that results in an inflammatory
response intended to remove sun-damaged cells.
We see and feel the process as sunburn.
“The
inflammatory response is important to start the process of healing
after cell death,” said Gallo. “We also believe the inflammatory process
may clean up cells with genetic damage before they can become cancer.
Of course, this process is imperfect and with more UV exposure, there is
more chance of cells becoming cancerous.”
Gallo
said it’s still not known how gender, skin pigmentation and individual
genetics may affect the mechanism of sunburn. “Genetics is closely
linked to the ability to defend against UV damage and develop skin
cancers,” he said. “We know in our mouse genetic models that specific
genes will change how the mice get sunburn. Humans have similar genes,
but it is not known if people have mutations in these genes that affect
their sun response.”
